1. Field of the Invention
The present invention relates to a sheet feeding cassette accommodating sheets of a recording medium (e.g., paper) and an image forming apparatus including the sheet feeding cassette, for example, a copier, facsimile, plotter, or printing machine.
2. Description of the Related Art
In a sheet feeding cassette of an image forming apparatus including a sheet feeding cassette accommodating sheets, a fence (side fence) that defines the position of the sheets perpendicular to a direction of sheet feeding is needed because the accuracy of the position of the fence directly affects a skew angle of the sheet feeding.
It is preferable that a light force is required to move the fence because a user directly operates the fence to accommodate various sizes of sheets.
The fence is also needed to be affixed securely at each setting position, and to move smoothly when the user changes the setting. Japanese Patent Laid-Open Application No. 2005-131861 discloses a sheet feeding cassette where a user can release the fence by pushing a button and the user can reengage the fence in a fixed state by pushing the button after moving the fence to a desirable position.
However, this sheet feeding cassette configuration has drawbacks because the pushing direction of the button and the moving direction of the fence are in discord. That is, use of the fence requires an unnatural user applied force to adjust the fence to an accurate position.
Japanese Patent Laid-Open Application No. 1999-139576 discloses a sheet feeding cassette where the user can release the fence from a fixed state by rotating a fixing portion perpendicular to the moving direction of the fence.
However, as discussed above, the sheet feeding cassette has drawbacks because the releasing direction of the fixing portion and the moving direction of the fence are in discord. Consequently, an unnatural force is required to adjust the location of the fence to an accurate position.
Japanese Patent Laid-Open Application No. 2005-053645 discloses a sheet feeding cassette where the user can release an engagement of a tooth portion positioned below the fence and the body of the sheet feeding cassette by pushing a lever and the user can fix the location of the fence by pushing the lever after moving the fence to a desirable position. This sheet feeding cassette is more preferable than the configurations described above because the pushing direction of the button and the moving direction of the fence are consistent with each other.
However, this configuration has drawbacks because a trench wall exists in the rotating direction of the tooth portion and the tooth portion strikes against the wall. Consequently, friction may occur and additional effort is required by the user to operate the fence.
In order to use a sheet P having variable widths, the user may move the side fence 9a, 9b to accommodate the sheet P. The fence is needed to fix tightly at the desirable position to avoid skewing. Further, the fence is needed to move smoothly when the user operates.
More specifically, Japanese Patent Laid-Open Application No. 2005-053645 and Japanese Patent Laid-Open Application No. 2004-315229 disclose a sheet feeding cassette having the fixing structure of the fence illustrated in FIG. 5.
As illustrated in FIG. 5, a fence 9 is controlled by a lever 15. The user pushes a knob 15a, positioned at the top of the lever 15, using a finger toward the direction of an arrow 16 to release the fence 9. A tooth portion 15b is provided at the bottom of the lever 15. The tooth portion 15b pivots upward in the direction of arrow 17 in response to pushing the knob 15a. Below the tooth portion 15b, a trench 19 is provided as part of the main body of cassette 18. The fence 9 can be fixed or released by engaging or releasing the engagement of the tooth portion 15b and the trench 19. The trench 19 is aligned at a predetermined pitch toward the moving direction of the fence 9.
FIG. 6 is a cross-section view showing the tooth portion 15b and the trench 19 at the engagement position. As illustrated in FIG. 6, the tooth portion 15b of the lever 15 pivots upward when the knob 15a is pushed by the user. The user can set the position of the fence 9 to the width of the paper “P” easily because the user can move the fence by moving the knob 15, and the direction of movement of the fence 9 is consistent with the direction of movement of the knob 15a. 
However, the direction of the releasing movement of the tooth portion 15b (i.e., the direction of arrow 17) is perpendicular to the vertical wall 19a provided in the trench 19. Consequently, the tooth portion 15b sometimes strikes against the vertical wall 19a of the trench 19, and the force necessary to release the fence becomes enormous.